If you subscribe to this idea - or even if you don't - the easiest way to come up with something that feels original is to take ideas you like and reskin them to fit the D&D world.

Here are four examples off the top of my head:

You like Indiana Jones? The PCs are action archaeologists racing to plunder a dragon's tomb before their mercenary rivals sell the loot to the highest bidder.

You like heist stories? Have your PCs break into a bank with all kinds of traps and wards and guardians, and give them time to plan and investigate the bank's blueprints and defenses by scouring city records and stealing information from the dwarven architects and archmage that built the place.

You like Die Hard? The PCs are visiting an eccentric wizard's tower for a demonstration of a cool new spell when the thieves' guild seizes the building and activates the magical lockdown and safeguards. PCs need to use guerilla tactics to take down the thieves before they complete their objective, while safeguarding the hostages.

You like Jurassic Park? The PCs are part of a small private tour of a new monster zoo on an island when something goes wrong and the monsters are set loose. As they try to make it to the ship on the coast, they uncover a conspiracy to sabotage the island for profit.

If that's not good enough, smash two or more ideas together and reskin them to be consistent with each other. Let's mash all four of those previous ideas together:

The party works for a museum that wants to recover a long-lost solid gold holy symbol of the sun god from a long-deceased dragon's hoard. Recently discovered maps place the dragon's lair on an island off the coast. They'll have to move quickly, because their rivals - a dwarf/gnome duo of mercenaries - got to the information first and plans to sell the holy symbol to the highest bidder.

But that's not all. The island has recently been bought and reworked by an eccentric wizard as an arcane zoo, featuring dangerous monsters from across the realm. It's not open to the public yet and security is very high - but there's a private tour for wizards only, and that's an opportunity to sneak in. The name tags for the tour group allow access to the park's teleportation circle network. Turns out that the mercenary duo had the same idea, and are also using the tour group as cover.

The park's security centre should hold all the information the party needs to bypass the wards and find the dragon's lair, but the building is heavily guarded and protected. The PCs will need to slip away from the tour group and find the park's plans in the security centre without being spotted, then decode the arcane script piece by piece as they make their way through the defenses. Once the players access the dragon's lair, they'll have to carefully pick their way through the ancient traps to find the hoard. The dragon was so greedy that the final trap animates its skeleton to protect is loot even after death. This is probably a good area for a confrontation with the mercenary archaeologists - they can either steal the holy symbol and force the party to chase them down, or the party gets the artifact and the mercenaries will hound them the rest of the adventure.

Upon exiting the tomb, all hell has broken loose. The zoo has been sabotaged and the monsters are roaming free; the network of teleportation circles is shut down. A few of the park employees have defected and are in the process of stealing the unique ward spells the wizard wrote to build the park. A group of thieves has taken the tour group and the wizard hostage and is sending out men to try to find a treasure hidden somewhere in the zoo - the artifact of the sun god. And to make things worse, a major storm is brewing.

The party's objective is simple - escape the island with the artifact. But now they have a whole slew of complications in their way: hungry roaming monsters, rogue employees, a coordinated thieves' guild, a rival archaeologist team, and a big storm. They also have two additional opportunities for heroism or loot in the wizard's spellbook and the hostage scenario.